Prospect, the union representing 34,000 specialist civil servants, demanded an immediate meeting with the Chancellor and said sacrifices on pay in the public interest should be shared equally across the public sector.
"Instead the government intends to respect multi-year pay deals, which will create a casino of winners and losers between those lucky enough to have a deal in place and those who will be frozen out," said Dai Hudd, Prospect Deputy General Secretary.
"In addition the government intends to discriminate against the civil service by cutting its pay to the bone while allowing other public servants to take home increases that are 1.8% higher."
Hudd said the attack on civil service pay was the third leg of a triple whammy, in addition to its policy of halving redundancy terms for civil servants and promises to slash thousands of jobs by efficiency savings over the next four years.
The complete failure to warn staff, let alone consult them before announcing the decision, was yet another sign of ministers taking their own employees for granted, said Hudd.
He added: "This is a crass policy on economic grounds. It will take money out of people's pockets just when the economy desperately needs the British consumer to increase demand for goods and services. It is a black day for fairness, for public service and the integrity of government."